1. Field of the Invention
This invention relates to a variable displacement engine that is capable of varying the number of operating cylinders by bringing part of the engine cylinders into an idling state during operation. More particularly, it relates to an idling controller that regulates and controls the idling condition of a variable displacement engine.
2. Description of the Prior Art
To prevent the generation of noxious gases through the improvement of combustion efficiency and to achieve better gasoline mileage by raising the load factor and, thereby, decreasing pumping losses, variable displacement engines of conventional designs cause part of their cylinders to idle while the engines are being run under low load by, for example, closing the intake and exhaust valves of some cylinders.
But there has been a problem of unstable operation with these conventional variable displacement engines. With their throttle valve opened to the same extent when the engine is running at idle, greater power is developed when only part of the cylinders are used than when all cylinders are operated. As a consequence, the revolutions of the engine crankshaft decreases as the partial-cylinder mode is switched to the all-cylinder mode without actuating the accelerator with no load applied, creating an unstable engine operation.
In contrast with this, when an engine that is operated with appropriate crankshaft revolutions in the all-cylinder mode is switched to the partial-cylinder mode, engine speed will increase excessively.
It is, of course, possible to maintain the all-cylinder mode throughout the idling period, attaching greater importance to the starting performance than to the fuel efficiency, or to maintain the partial-cylinder mode when importance is placed the other way around. But this practice cannot be implemented without sacrificing either the starting performance or fuel efficiency.